The use of powdered metal (PIM) parts (powder injection molding manufacturing process) has accelerated in recent years for components difficult to manufacture by machining, and can offer a cost-effective alternative to other metal forming processes. Advantages of powdered metal manufacturing process include lower costs, improved quality, increased productivity and greater design flexibility. These advantages are achieved in part because powder metallurgy parts can be manufactured to net-shaped or near-net shape which in turn means little material waste, and also eliminates or minimizes machining. Other advantages of powdered metallurgy manufacturing process and parts produced therefrom, particularly over other metal forming processes, include greater material flexibility including graded structures or composite metal structures, lighter weight parts, greater mechanical flexibility, reduced energy consumption and material waste in the manufacturing process, high dimensional accuracy, good surface finish, controlled porosity, increased strength and corrosion resistance of the parts, and low machining costs, among others. However, production of high quality powder metal parts is dependent in large part on the quality of the powder metal. The smaller the metal particles and the more uniform the particles are in size and shape, the fewer voids and surface imperfections in the finished product.
Also, because the rate of diffusion is inversely proportional to the square of the particle size, shrinkage and densification of porous powder parts proceeds much more rapidly by minimizing particle size, with remnant pores in the formed part being smaller. Typical particle size used for injection molding are in the range of 0.5-20 μm and about 20-40 μm in the case of conventional powder metal processes, and presently are made as round spherical powders. See Erickson et al, Metals Handbook, Ninth Edition, Volume 7, Powder Metallurgy (2007) Injection Molding, pages 495-500.
Solid free-form fabrication (SFF) or so-called “3-D” printing of metal parts also has accelerated in recent years. So-called “3-D” printing” (also known as Rapid Prototyping and Manufacturing (RP&M)) is a method of creating three-dimensional objects by depositing or forming thin layers of material in succession so as to build up the desired 3-D structure. The process has some similarities to normal printing in that a digital representation of an object to be formed is used and each layer is formed as if it were one layer of printing, e.g. by moving some kind of printing head over a workpiece and activating elements of the printing head to create the “printing”. Various methods have been devised to create the thin layers.
There are many items which can be produced by 3-D printing. However, until recently, most materials used in 3-D printing were polymerizable materials. As a result, the final product is not very strong or heat resistant, and 3-D printing heretofore primarily has been used in prototyping. However, recent advances in metallurgy have provided metal powders that can be used in 3-D printing of parts. In one technique metal powder is dusted onto a substrate and the powder coalesced by some means, e.g. by heating laser beam or electron beam, in accordance with the shape of the cross-section of the object to be formed. Yet another method involves dispensing drops of molten material at an elevated temperature which then solidify on contact with the cooler work piece.